After drilling a wellbore in the oil and gas industry, the drilled wellbore can be subsequently completed by cementing a string of metal pipes connected end-to-end within the wellbore. Commonly called “casing,” such pipes increase the integrity of the wellbore and provide a flow path between the Earth's surface and selected subterranean formations. Some wellbores are lined with multiple concentrically positioned pipes (i.e., concentric strings of casing). Moreover, in some wellbores, one or more production pipes are extended into a cased wellbore to provide a conduit for hydrocarbons to be conveyed to the earth's surface. Accordingly, as used herein, the term “pipe” or “wellbore pipe” will refer to metal pipes or pipelines that line the walls of a wellbore (e.g., casing) but may also refer to a string of production pipes or tubulars extended into a wellbore.
During the lifetime of a well, wellbore pipes are exposed to high volumes of materials and fluids required to pass through them, including chemically aggressive fluids. In harsh environments, the pipes may be subject to corrosion that may adversely affect their functionality over time. Consequently, the structural integrity of wellbore pipes may change over time due to chemical and mechanical interaction. Moreover, due to the length, volume, accessibility difficulties, and long time periods associated with the process, it is a costly task to monitor wellbore pipes and pipelines and intervene when required.
Electromagnetic (EM) sensing technologies and techniques have been developed for such monitoring applications and can generally be categorized into two groups: frequency-domain techniques and time-domain techniques. In frequency-domain techniques, measurements of the wellbore pipes are typically performed at high frequencies to characterize the innermost pipes and at low frequencies to characterize the outermost wellbore pipes. Time-domain techniques are based on the pulse eddy current and employ the transient response (decay response versus time) of the pipes to a pulse excitation. Proper analysis of the signal responses can determine metal losses in the pipes with better resolution, and improve the robustness of the characterization process to noise.
Visualization of the inspection results helps facilitate a more accurate evaluation of the wellbore pipes, which can lead to informed decisions about how to address the current condition of the pipes. The ultimate goal is to have a proper assessment of the current condition of the wellbore pipes so that, if needed, repair or replacement strategies can be implemented in a timely manner.